Preheat oven to 180°C.
Process biscuits to fine crumbs in a food processor. Add butter and whiz to combine. Press evenly into the base of a 20cm springform cake pan and chill while you make the filling.
Place cheese, thickened cream, eggs, 100g caster sugar and 1 teaspoon of vanilla bean paste in the (cleaned) food processor, and process until smooth. Spread filling over biscuit base.
Bake for 30 minutes or until filling has set. Remove cake from oven and set aside to cool for 15 minutes.
Meanwhile, combine sour cream, yoghurt, another 50g caster sugar and remaining vanilla paste. Spread over cake, then return to oven for a further 10 minutes. Set aside to cool, then refrigerate for at least 4 hours or overnight.
Place remaining 50g sugar, cranberries and port in a saucepan over low heat. Cover and cook for 5 minutes. Remove lid and stir.Continue to cook until the cranberries give off their juice. Stir arrowroot into a dash of the juice, then add to pan with berry mixture and continue to cook until the mixture thickens. Remove from the heat and cool.
To serve, top cake with cranberry sauce and garnish with the dusted rosemary sprigs.
